Hum from amp and CD player

Likely due to increased power demands at peak times. Folks come home after work and run appliances. More noise on the grid. The transformers in your gear react to this noise. As well it could be the increased power consumption and resultant noise in your own home.

I wonder if you are running something in the evening, such as the dishwasher? A dedicated mains supply usually fixes this, as well as potentially giving better sound quality. 

Don't have a dedicated mains supply but do use an Isotek Aquarius power conditioner.

Try listening without the conditioner, which often reduce the sound quality of Naim systems, reducing drive and dynamics. It's worth trying to track down what appliance is causing the hum, unless it's coming from outside the house of course. 

Will do, but my experience is that the Isotek makes a noticable improvement  to the sound quality.  That said, I'm pretty sure my mains supply is far from clean.

The hum is most likely to be caused by a very specific type of mains waveform distortion, where one half of the mains cycle is being loaded more than the other.  This means that the half cycle (it could be the positive or negative one) is being pulled down a little, it's only fractions of a volt, but that's enough to unbalance the sine wave.  The net result is that the current produces an unbalanced magnetic field in the transformers, and as that builds up (less than 1 second needed) they start to hum.

This waveform distortion can be caused inside your own house or can come from outside.  To test if it's inside your house, wait for it to get bad and then switch off everything else in the house.  If the hum remains, then it's coming from outside.

If it's coming from inside you can change the offending appliance for one that's better designed or try a dedicated mains supply as HH suggests.

If it's coming from outside, then the best thing is to use a balanced isolation transformer driving a dedicated mains supply to the HiFi.  Get a sparky to put the isolating transformer near the CU (Consumer Unit - previously known as the fuse board!) and wire it in CTE (Centre Tap to Earth).  We can offer more advice here if needed.  There are some plug-in mains 'DC blockers' available that also work (amongst others, Isol8 and Isotek make them), but they are quite expensive.  (I did a DIY version of one of these to cure my problems, but I can't discuss that here, as discussion of DIY mains stuff is contrary to forum AUP.)

I agree with HH to try it without your Isotek,  it might be that it makes a difference to sound quality & conversely it might be that the Naim forum is adamant about some so called conditioners causing a negative effect on sound,  but you need to do this.

However a variable transformer hum such as you describe is indicative of DC Offset a form of sine wave distortion,  this can be caused by something in your property or something in the neighbourhood.  Tracking the source down is something you can do easily in your property, its normally something that runs with a reduced power feature so try switching off fridges, old/defective light dimmer switches, heating/cooling pumps/fans etc.    Finally not all Isotek devices can deal with DC Offset & it might be that you need to consider changing to one that can.      So the question is what Isotek do you have ???

Thanks for the detailed response Hugh and Mike-B.

It is an Aquarius EVO3.

Have a look at Isol-8's Powerline Axis -- fixed my evening transformer blues. Quite expensive though... It's without the mains conditioning that is so heavily disapproved here -- just fixes the DC offset. And once the hum is gone for a while, you forget about the price of the Isol-8... 

Rotifer217 posted:

.............    It is an Aquarius EVO3. 

Ah OK,  sorry but that does not filter DC Offset.     Have a look at EVO3 Syncro,  this is specifically made for DC Offset, but I'm not sure that Isotek include a DC filter in any of their 'conditioners'.    Other brands may do so,  but I really do not believe in 'conditioners',  IME they don't do much other than dull down SQ,  this is something a DC filter does not do  (see my profile)  

I suggest you start by turning off all the power items to see if the culprit lives in your house is the best first move,  then decide on the next course of action.   

Thankyou everyone for your advice.

Problem solved.  It is the electric blanket.  Turn it off at the wall and the hum disappears.

Ah yes, electric blankets are notorious.  

Electric blanket??!! Looks like you need more PRAT... 

Rotifer217 posted:

Problem solved.  It is the electric blanket. 

  And a MUCH cheaper solution than an IsoTek Synchro.

By the way, I forgot to ask:  How may cells do you have?

I'd have though it has to be more than 217; most rotifer species have about 1000 cells.

For me it was the boiler. When my old one was timed to go on, she always made me hum.    Turned out it was the timer unit.

Speaking of which... my other half has just ordered a few of these..

Spider repellent devices. Hope they don't cause hum and mains nasties !!

Can it even be the neighbours electric blanket?

TOBYJUG posted:

Speaking of which... my other half has just ordered a few of these..

Spider repellent devices. Hope they don't cause hum and mains nasties !!

 

You may well have bigger problems to worry about...

TOBYJUG,

I've used these devises for about 3 years, I can't say i've heard any negative affect on sound quality, don't see too many eight legged buggers either.

Karl

Hilary hates spiders. Can you recommend a spider deterrent that works? As it's September they will be getting ready to invade...

TOBYJUG posted:

Speaking of which... my other half has just ordered a few of these..

Spider repellent devices. Hope they don't cause hum and mains nasties !!

I've had a similar device for several years now. It has different settings intended to deter different beasties - I bought it to keep mice out, and it seems to work quite well.  They work in two different ways, by emitting an ultrasonic noise into the room they are in, and by putting an electromagnetic signal onto your mains wiring, the latter being intended to cover the whole house. I'm not overly happy about the idea of polluting my mains with a known source of EMI, but in practice, it doesn't seem to have any noticeable effect on sound quality. 

ChrisSU posted: 

 .............................   it doesn't seem to have any noticeable effect on sound quality. 

I had one for a while when we had an arachnophobe still at home,  didn't have much effect on spiders either.   

Hungryhalibut posted:

Hilary hates spiders. Can you recommend a spider deterrent that works? As it's September they will be getting ready to invade...

Hanging a big hairy plastic one inside the front door is usually a good deterrent to arachnophobes.

Oh, hang on a minute, you actually want to deter the spiders not the arachnophobe!  .